Why would you want to store the password and use because if you refresh environment you are going to have the same and all old instances still going to use the old value where process was in execution stage. The best would be to use the PPM session to authenticate and execute.

1) Try to carry out a simple XOG directly, using the preferred username and password and check if that succeeds

2) If you are running the a XOG through a script in the process, then check the script. Ideally, the script could pick up username from session / properties.xml , however check if any username is hard coded in the script, or check the reference of the username in the script.

samik has already provided to get user session ID by passing username. not password.

For best practice,

Don't pass user name and password in the gel script to get XOG session ID. if you using this solution, better to change the solution to get XOG session ID by passing XOG user name only. this will help to avoid Process failure whenever password getting changed.